Field of the Invention
The present invention relates to the area of the separation of immiscible fluids of different densities.
It may be applied in particular to problems concerning the separation of oil and water in crude oil emulsions, whether in the area of petroleum production, refining or decontamination. It may likewise find an application in the separation of greases in the environment, in the extraction of free gases in one or more liquids, in the treatment of rainwater or in the production of olive oil. In particular, it may find an application in the separation of the phases of an emulsion comprising a majority fluid, referred to as a carrier fluid, in which droplets of a secondary fluid are present.
Description of the Related Art
In order to carry out this operation, the use of gravity separators is well known, into which the emulsion is introduced at one extremity of a reservoir such that, after a sufficient residence time, the drops of the secondary fluid of the emulsion increase or decrease depending on whether their density is lower or higher than that of the carrier fluid. Two superimposed layers of the two fluids are thus created at the extremity of the reservoir, the lighter fluid being above and the heavier fluid being below, which fluids are pumped by appropriate means.
Gravity separators suffer from the major shortcoming that they require very long separation periods. It has been estimated that a period of 5 minutes is required, for example, in order for a drop of oil having a diameter equivalent to 200 micrometers, having a density of 0.85, to rise to a height of 1 m in still, fresh water at a temperature of 20° . Furthermore, gravity separators are bulky, heavy and expensive. As a result, they are incapable of being moved or transported on lightweight and rapid platforms, such as hovercrafts, whose use is particularly well suited to the treatment of oil spillages in zones which are not readily accessible, such as wetlands.
The use of rotary separators with a centrifugal effect, which allow much shorter separation periods than those of gravity separators to be achieved, such as fixed cyclones, rotary cyclones and centrifuges, is also well known. In the current embodiments, these rotary separators are generally complex in nature and are also very heavy, bulky and very expensive. Furthermore, they do not lend themselves readily to being moved or transported.
A separator with a centrifugal effect is described in particular in the patent published under the reference number WO95/26223. This separator comprises a rotating drum defining a compartment exhibiting an axial inlet for an emulsion at one extremity, and inside which there are arranged, for a first length, radially extending longitudinal paddles, followed, for a second length, by a porous cylindrical coalescence body formed by rolled coils of mesh or layers of mesh. This drum comprises, downstream of this compartment, annular overflows intended for the extraction of the liquids, separately, and axial passageways intended for the discharge of the separated liquids. This separator exhibits, in particular, the disadvantages of being very limited in respect of the ratios between the densities of the liquids in the emulsion to be treated and the volumetric ratios of the liquids in the emulsion to be treated, and of becoming clogged rapidly.
Another separator with a centrifugal effect is likewise described in the patent published under the reference number WO 93/25294. This separator comprises a rotating drum of truncated conical form defining a compartment exhibiting an axial inlet for an emulsion at its smallest extremity, and comprises, downstream of this compartment, annular overflows intended for the extraction of the liquids, separately, and axial passageways intended for the discharge of the separated liquids. Arranged in a first section of said compartment, far away from its downstream extremity, are radially extending longitudinal paddles, the stated purpose of which is to permit an axial alignment of the emulsion. However, these vanes exhibit the disadvantage of generating a considerable shear effect during rotation of the drum and circumferential percussion of the emulsion, contrary to the desired object of the separation of the liquid.